Method of sinking tubes



@NITE srmas mrsm orricn METHOD OF SINKING TUBES Samuel E. Diescher, Pittsburgh, Pa., assignor to I Dlescher Tube -Mills, Inc., Pittsburgh, Fa., s-

corparation of Delaware Application August e, 1932. Serial No. 62*?,718

4 Claims. (Cl. so -s2) Myinvention pertainstomethods of sinking and the top of the groove) does any roll movetubes, that is tosay performing upon tubes the at a peripheral speed equal to the longitudinal operation of reducing their external and internal speed of the tube. The portions of the grooved diameter by. the application of exterior pressure surfaces of each roll from the pitch plane* to in a direction which is, broadly speaking, radial the top of the groove move faster, and the porof thetube. ti ons from the pitch plane to the bottom of In a common method oi' sinking tubes a series the groove move slower, than the tube. The

' of pairs of grooved rolls are employed, the rolls result is `a relative sliding movement, between constituting each pair being opposed and set with the rolls and the tube, which causes rapid wear their -axes parallel and at right angles to the of the rolls. As has been said,'such wear cannot direction of movement of the tubes so that there be taken up by adjustment. 6 is enclosed between them a space which is .of Third-Even though the finished tube be circua 'generally circular character, though not often lar outside,-a result in itself difllcult to obtain absolutely circular. The circumference of this by the method under consideration,-it is not space is less than that of the tube entering the` circular inside. This is because any one pair or particular pair oi rolls, so that the tube is comreducing' rolls compresses 'and deforms the metal pressed by the rolls and its external and internal' of the tube in or about a plane passing between diameters' are reduced. The shaping of the the rolls, thickening the walls of the tube to a grooves of the rolls is such that* the space begreater extent in or about this plane than else tween each pair is les'sthan that between the where. When the tube passes through asucceedl preceding pair of the series, the result being ing pair of rolls, the plane between which is at an h that the tube, in passing through the successive angle to the plane between the preceding pair, any pairs, is progressively reduced until the desired exterior protuberance produced by the first pair external diameter' is reached. The successive of rolls is compressed into line with the remainder pairs of rolls are disposed so that the axes of of the surface of the tube, but, because. of the the rolls of 'any pair extend at an angle to wall having been thickened in that region, only the axes of the rolls of the next pair, usually at the expense of a corresponding interior proat right angles. The rolls are disposed m this tuberance. 'The result, therefore, is .that the manner with the intention that any deformati finished tube has a number of small interior longlof the tube, by one pair of rolls, in or about ud thickenings, ausing, under hea y reducthe plane .between sucnrolls will be rre ted tions, the bore of .the tube to tend to assume a by a succeeding pair of rolls, the plane b t rectangular shape... In order to lessen this diswhich will be atan angle to the plane between advantage, and also the disadvantage arising the 'first pair. As far as exterior shape is confrom the relative sliding movement between the cemed, the results obtained, in this respect, are rolls and the tube, it has b p p s t0 p y, reasonably satisfactory', though shaping rou instead of the pairs of reducing rolls, what are succeeding the train of reducing rolls, are usually' known s "W rolls, h is t0 s sroups f required to bring the sunktube to a final ex= four rolls embracing the tube. But the resulting terior shapeas nearly circular as possible. machinery is ex e y complex, d, in any The .foregoing ethod of sinking tubes has case, the troubles are only reduced, not eliminated. 95

a many drawbacks, the majority, and perhaps all,. Fourth-Shoe the tube is being operated upon of which occur also in the practice of other by a number of pairs of reducing rolls simultane- ;inking methods. The following are some of these ously as it passes through the sinking mill and is drawback& a somewhat reduced and elongated by each pair,

First-4a order to obtain a given reduction the various pairs of rolls should be driven at corot external diametenthe tube must be passed respondlngly difierent relative speeds. It is through a relatively large number of reducing practically impossible to drive the rolls at exactly rolls, followed by shaping rolls. These are exthe right relative speeds. Therefore, since longl-` pensive to maintain, especially as wear of the tudinal compression of the tube between succesroll-faces can not 'be taken up by 'adjust-ments, sive pairs of rolls would be undesirable, it has been 5 it being necessary to regrind the rolls when they the practice to set the relative speed of the rolls -`become materially worn. so that the tube is under some-tension between the Secondmie wear on the grooved roll-faces successive pairs of rolls. This resultsina 'stretchis heavy.. This 'is largely because only in its ing of the tube, and such stretching of the tube pitch plane (a plane intermediate the bottom resultsin the finishedtubehaving a portion at no loo cut off, with a resulting considerable waste of material and labor. 4

It is the object of my invention`to provide a method of sinking tubes which will avoid the above-mentioned and other drawbacks which have characterized, not only the common method v of sinking above-referred to, ,but such other sinking methods as have come under my observance; which will permit tubes to be sunk rapidly, sometimes by a single pass through the rolls and always with much fewer passes than have heretofore been necessary; which will permit, for its practice, the use of apparatus capable of operating on and/or producing tubes of a variety of diameters merely by adjustments of such apparatus; and the practice of which will produce a tube that is truly circular, bothwithin andwithout, and is of uniform thickness from one end to the other.

I obtain the above object by applying to the tube to be sunk the pressure of cross-rolls (which term, as used herein, is intended to include other rotating pressure members adapted to rotate the tube about its axis), such as are used in the piercing of billets and the elongating of tubular blanks, and at the same time confining the tube between the cross-rolls by surfaces moving in the direction of the longitudinal movement of the tube.

In piercing billets and inreducing wall thickness of and elongating tubular blanks, a mandrel is employed in conjunction with the cross-'rolls, and the metal against which the cross-rolls press is supported interiorly against such pressure by the mandrel. In sinking, however, no such interior support exists, and the pressureon the tube is limited to that which can be resisted by the tube itself. It has been sought heretofore to sink metal tubes in cross-rolling mills, but the efforts which have been made to do so have not, so far as I know, met with success. One reason for the failure to efiect substantial sinking of tubes by cross-rolling has been, as I believe, that, unless the tubes have very thick walls as related to the tube diameter,-a condition in which a sinking operation is hardly likely to be needed,--the grip of the cross-rolls on the unsupported wall of the tube cannot be sufficient to rotate and advance the tube against the frictional resistance of the fixed guides used for confining the tube between the rolls. Furthermore, even. had the process been successful otherwise, the decrease of tube diameter, would have gone into increase of wall thickness to such an extent as to lessen the value of the process.

Tubes are sunk successfully by cross-rolling, according to the present invention, by reducing the peripheral friction between the tube and the guides, and pulling the tube forward in the direction of its movement longitudinally through the fine the tube at the place where it is subjected to the reducing pressure of the cross-rolls, and by friction between the tube and the guides may be greatly reduced or even substantially eliminated, with the result that the rotating tube enters and passes freely between the guides and any such resistance to rotation of the tube by the guides as would interfere with the desired rotation of the tube by the rolls is prevented, and at the same time not only is longitudinal frictional resistance to the movement of the tube through the pass entirely avoided but the moving surfaces of the discs exert a positive forward pull on the tube, tending to accelerate its longitudinal movement through the pass. Moreover, the pulling action of the discs on the tube during the sinking operation results in a certain flow of the metal in a longitudinal and forward direction during the helical movement of the tube, with the result that the reduction of the diameter of the tube goes more into increased length and less into increased wall-thickness'than would otherwise be the case.

I have heretofore pointed out that if the peripheral speed of the guide disc is made to equal approximately one-half the peripheral speed of the work-piece (the tube) divided by the sine of the average angle of the helix of feed of the workpiece' through the pass, the condition under which frictional resistance peripherally of the work-piece is theoretically eliminated will obtain, provided the axis of rotation of the guide disc is perpendicular to the axis of the tube or other work-piece. The reduction of the peripheral friction is greatest during the first stages of the increase in speed of the guide disc and is but slight during the last stages as the speed approaches the theoretical figure of the formula; so that speeds much less than the formula speed are often sufficient for successful results.

The invention thus comprises a method wherein the tube is sunk by applying to successive portions thereof circumferentially acting forces which press inward the interiorly unsupported wall of the tube and rotate the tube and other, longitudinally acting, forces which confine the tube and pull it longitudinally forward.

My improved method is particularly adapted for the sinking of tubes having relatively thin walls. This operation, as stated above, has not been accomplished hitherto by means of crossrolling because of the inherent difficulties encountered in the methods heretofore available.

In the present method the tube of thin walls that are entirely unsupported interiorly traverses a pass formed by surfaces moving in several directions and which confine the walls of the tube to such extent that the diameter is reduced and, at the same time, the tube is rotated and is moved longitudinally by the moving surfaces. The longitudinally movable surfaces pull the tube longitudinally to divert the reduced cross-sectional area into elongation and thus at least partially offset the tendency. of the mill to thicken the walls of the tubes as the diameter is reduced by the pressure surfaces.

The practice of my invention will be the more readily understood by reference to the accompanying drawing, in which Fig. 1 is a side elevation, partly in section, of a cross-roll stand with a tube under sinking treatment in place therein, and Fig. 2 is a section on the line n--II of Fig. 1.

In the drawing, the reference characters 10 and 11 designate a pair of helically acting crossrolls, mounted on driven shafts loa and Ila. respectively, dispo'sed at an angle to each other and to the line of feed of a tube between them. They are shown as of '*barrel" shape, but they mightvbe of any other of the several shapes well known in cross-roll operations, and their place might be taken by discs operating helically in a manner that is also well known. Between these cross-rolls, which are rotated in the direction indicated by the arrows, the tube b to be sunk is entered. The tendency of the cross rolls is to .force the tube from a circular into an oval crosssectional shape, and this is restrained by confining discs 12 and 13 mounted on shafts 12a and 13a and disposed in or about the plane intersecting the space between the rolls 10 and 11. The

. cross-rolls, being unable, because of the confining discs, to force the tube into the oval form which would correspond with the narrowing space between the cross-rolls on the entering side thereof, the tube is reduced in diameter and increased in length The conning discs are driven in the directian indicated by the arrows, i. e., to move in contact with the tube in the direction of the longitudinal movement of the tube, at a per-ipheral speed in excess of the speed of longitudinal movement of the tube, in order to reduce frietion peripherally of the tube between the latter and the confining discs and to pull the tube forward. As shown, the distance, c, between the confining discs at their closest points is equal to the width of the threat of the rolls, i. e., the distance, d, between the cross-rolls at their closest points. In those circumstances, and the confining discs being disposed, in `the example shown, so that a plane including their axes passes through the threat-of the rolls, the tube will be maintamed circular while in the throat of the rolls. The confining discs may, however, be adjusted otherwise than as shown,- for instance, somewhat wider apart so as to permit some ovality of the tube when the latter is confined 'in the shortest space between them. This will lesson the reduction of tube' diameter, for any given setting of the cross-rolls, but has the advantage of providing a ready means for precisely controlling the diameter of the product without resorting as well to an adjustment of the cross-rolls. In thus variously placing the discs, bath as to the distance separating them and in other respects, apparatus according to the invention of my co-pending application Serial No. 631,511, filed September 2, 1932, may be employed.

By the method of this application I am en abled to reduce tubes very considerably in a single pass through the cross-rolls,--as much, for instance, as would require a number of passes through the grooved rolls of an ordinary sinking mill. Mer-cover, the resulting tube is perfectly circular both inside and outside, and is of uniform wall thickness from one end to the other. By simple adjustment, the same mill becomes available for vad'ying diameters of wor piece and/or product, and wear of the rolls or discs can be readily taken up. The method is applicable to the sinking of tubes either in the hot or the cold state.

I claim:

1. The method of sinking tubes, which comprises subjecting the tube to forces acting on opposite sides of successive portions thereof to press inward the interiorly unsupported wall of the tube and to rotate the tube, and simultaneously subjecting the successive portions of the tube to other forces acting to confine the tube exteriorly and to pull the tube longitudinally forward in the pass.

2. The method of sinking tubes, which comprises subjecting the tube to the action of helically acting cross-rolls bearing on opposite sides of the tube with the wall of theitube unsupported interiorly against the pressure of the cross-rolls, and exteriorly confining the tube between the cross-rolls and pulling it forward in the pass by surfaces moving in the direction of longitudinal movement of the tube and at greater speed.

3. The method of sinking tubes, which comprises passing an interiorly unsupported tube through a pass of smaller diameter than the tube formed 'in part by moving surfaces having a movement principally in the direction to rotate the tube about its axis and in part by moving surfaces having a movement principally in the direction of the longitudinal movement of the tube through the pass.

4. The method of sinking tubes, which comprises passing an interiorly unsupported tube through a pass of smaller diameter than the tube formed in part by surfaces of cross-rolls set to rotate the tube about its axis and in part by moving surfaces having a movement principally in the direction of the longitudinal movement of the tube through the pass. 

